My room has very weak WIFI signal, and sometimes my smartphone will switch to the 4G network automatically. I remembered one night I watched a movie and on the next day I could not access the 4G network again because the data limit had been reached!
I had a idle router Linksys WRT310N, and the firmware had been flashed to DD-WRT, so I thought maybe I could place it in the living room and did some configurations so it could connect to the existing router, and then I could connect to it in my bedroom to get better and more stable signal.
There is a wonderful post about this issue: Repeater Bridge. I had spent two days and failed before I found this post, and almost gave it up.
For me the most important point is:
WPA Shared Key is the same for all the interface, including the created virtual interface.